An energy resolution of ΔE=12 eV [full width at half maximum (FWHM)] has been measured for the Mn55 Kα1 line (E=5.9 keV) using a superconducting lead absorber (90×90×1.3 μm3) readout by a single aluminum superconducting tunnel junction (100×100 μm2). The total detector area has been illuminated, while a slit mask of 150 μm width was used to partially shadow the detector leads and substrate area from impinging x rays. The total electronic noise contribution was measured as ΔEelec=4 eV (FWHM). The superconducting tunnel junction is located on a Si3N4 membrane of thickness 0.3 μm, the lead absorber is separated from the superconducting tunnel junction’s top layer by a thin layer of natural aluminum oxide. No deviations from linear energy response were observed in the energy range between E=1.74 keV and E=6.49 keV. The same resolution was obtained for a single aluminum superconducting tunnel junction, where the influence of substrate events was suppressed by a metallic buffer layer between tunnel junction and substrate. The escape of recombination phonons into the substrate causes small nonlinearities in the tunnel junction’s energy response.

We are developing cryogenic detectors based on Ir/Au phase transition thermometers and superconducting aluminium tunnel junctions for different applications, where a high-energy resolution and a low detection threshold is required. These applications comprise low background experiments such as CRESST and GNO as well as high-energy resolution X-ray spectroscopy for astrophysics and fluorescence analysis where energy resolutions below 30 eV (FWHM) at 5.89 keV were achieved.

The energy resolution of aluminum superconducting tunnel junctions (Al-STJs) has been improved by the introduction of a metallic buffer layer underneath the junction. When irradiated by 5.9 keV X-rays, a resolution of 12 eV (FWHM) was achieved for a junction size of 100×100 μm2. A mobile refrigerator system allowed to characterize these devices at the PTB-beamlines of the electron storage rings Bessy I and Bessy II. They showed linear energy response in the range between 200 eV and 6.5 keV and a strong increase in reduced energy events if irradiated at X-ray energies below the Al absorption edge at 1.56 keV.

Cryogenic detectors based on iridium-gold phase transition thermometers are being developed for various applications in astroparticle physics, aiming at high energy resolution, low energy threshold and moderate count rates. A microcalorimeter with an energy resolution of 15.5 eV (FWHM) for the Mn-55 K alpha(1) x-ray line for tentative use in an analytical x-ray system (e,g, SERI, TRFA) is presented. Copyright (C) 1999 John Wiley & Sons, Ltd.

We have been developing cryogenic detectors for astro- particle physics applications including search for Dark Matter, neutrino physics and x-ray astronomy. Most recently we started the development of high resolution x-ray detectors based on superconducting tunnel junctions and superconducting phase transition thermometers/transition edge sensors for microanalysis applications. Both types of sensors are being investigated as well as the cryogenic setup for applications on a scanning electron microscope.

We are developing both superconducting tunnel junctions and phase transition thermometers for high resolution x-ray spectroscopy. A resolution of 12 eV has been achieved for aluminum tunnel junctions when irradiated by 5.9 keV x-rays. These devices show linear energy response in the range between 200 eV and 6.5 keV. Phase transition thermometers consisting of an iridium/gold bi-layer and a gold absorber gave a resolution of 15.5 eV at 5.9 keV. The application of both sensor types is facilitated considerably by the use of an ADR cryostat. This mobile system allowed to characterize tunnel junctions at the Bessy I synchrotron.

Cryogenic detectors with superconducting tunnel junctions can provide an energy resolution improved by at least one order of magnitude compared with standard semiconductor detectors. While the detection principle was already demonstrated many years ago, the past years were dedicated to the transition from the laboratory sample to practical detectors. Our most favored detector design gives rise to tunnel junctions with electrodes of unequal energy gaps. In such hetero tunnel junctions bias conditions can be established which cause a negative signal current. We report the experimental verification of this effect, and we discuss the yield of charge signal of cryogenic detectors based upon superconducting tunnel junctions.

We fabricate X-ray detectors based upon superconducting Ta/Al/AlxOy/Al hetero tunnel junctions. Device characteristics are significantly influenced by the fact that the gap energies on the two sides of the tunnel barrier are not equal. We present experimental data showing the dependence of signal height and polarity on bias voltage in heterojunctions. The best energy resolution obtained in a single Ta/Al/AlxOy/Al heterojunction is 60 eV at 1.487 keV. We also report the observation of correlated signals from two separate tunnel junctions attached to one common Ta absorber strip.